Many mistakes are made when spot colors are mixed in with 4 color process (CMYK) colors and then sent to press. It’s actually quite common for companies to save money by running a large 4 color process (CMYK) print job and then ‘overprinting’ the stock with spot color black ‘text only’ plates. I work with a number of publishers producing multiple-language books who use this technique. They overprint different black language plates onto the same pre-designed color books. When this happens it is the responsibility of the designer to ensure that all overprint settings are correct and that all text has been colored with the ’5th color’ swatch (usually with black set up as a spot color).

Spot color printing creates brighter, more vibrant results, but with a smaller color range. When printing in single (spot) colors, a single color ink (normally with a Pantone reference number) is applied to the printing press roller. If there is just one color to be printed, there will be a single plate, and a single run of the press. If there are two colors, there will be two plates and two runs, and so on. The colors are layered onto the paper one by one.

Spot color printing would be typically used for jobs which require no full color imagery, such as for business cards and other stationery, or in monotone (or duotone etc) literature such as black and white newspaper print.

Pantone LLC, a wholly owned subsidiary of X-Rite, Incorporated, is the world-renowned authority on color. For more than 45 years, Pantone has been inspiring design professionals with products, services and leading technology for the colorful exploration and expression of creativity.

4 color process printing involves the use of four plates: Cyan, Magenta, Yellow and Keyline (Black). The CMYK artwork (which you will have supplied) is separated into these four colors – one plate per color. The four CMYK inks are applied one by one to four different rollers and the paper or card (‘stock’) is then fed through the printing press. The colors are applied to the stock one by one, and out comes the full color (4 color process) result.

Here is an example of 4 color process printing and three examples of spot color printing. There is a lot of versatility in designing for a spot color print run – experiment and see what results you can achieve!

CMYK Printing example:

If you look at a full color magazine through a magnifier, you’ll see that all the colors are made up of CMYK patterns, as shown by the above image. If you look at an area of spot color through a amgnifier, there will be no screen – it will show an area of solid, unbroken color (unless the grayscale or bitmap image it is applied to has a halftone screen of its own).

So How Does This Apply to me?

This means that the artwork you produce either has to be spot color artwork or CMYK artwork. Never, never NEVER produce RGB artwork. There is no such thing in the world of print. RGB (Red, Green, Blue) is a screen color mode and should only ever be used on screen for websites, video and other such screen based applications.

Never create final artwork destined for print with RGB images in place, or with RGB color swatches in use. It’s as simple as that. If you do, the printed result will be utterly unpredictable. Don’t let your color inkjet or laser printer fool you into thinking that if it prints out OK on them it’ll be OK for press. It won’t be.

Halftones For Printing

Because they cannot vary the thickness of the film of ink in highlights and shadows, lithographic printing presses are unable to reproduce the continuous tones of original photographic images. However, if the original image is first converted into a pattern of dots, the press can print a simulation that “tricks the eye” into seeing what appear to be continuous areas of ink coverage. An image converted in this way is called a halftone. Halftones are produced by screening the image mechanically or digitally to create the matrix of dots. The image is screened once for each color to be printed, so that a halftone for a four-color (CMYK) image will consist of four screens as shown here.

The Halftone Dot

Although we speak of offset lithographic plates as “planographic” or flat, the dots that make up the halftone images on them have substance and dimension. This highly magnified image shows an elliptical dot on the surface of the plate. On press, the dot will attract ink while repelling the water-based fountain solution that coats the plate in the non-image areas. The fountain solution repels ink to keep images from forming where they are not wanted.

Conventional Screening

Every halftone image consists of overprinted screens, one per color to be reproduced.

In conventional halftone screening, the sizes of the dots vary, but the spacing between them does not. The distance from the center of one dot to the center of an adjacent dot is always the same, regardless of size or location. The size of the dot depends on the density of the image area in which the dot occurs. Highlights contain small dots; midtones, medium-sized dots; and shadows, large dots.

PAPER:

CHOOSING AND USING PAPER

DESIGNING BY PAPER SIZE is the key to holding paper costs to a minimum. The idea is to impose as many pages or layouts on one sheet as possible so that you are not paying for paper that’s running through the press without having anything printed on it. Unprinted paper = paper wasted = money thrown away. Whenever possible, products should be designed to fit the available paper size. It’s usually a mistake to design the piece first and then select the paper it will be printed on.SPECIFYING AND BUYING PAPER are tasks that can be left up to the printer, or, if the quantity is large enough, handled by customers who want to be sure they are getting the best price. High-volume users like publishing companies often will insist on doing the buying themselves by dealing directly with the source.The “source” generally will be a paper distributor or paper merchant, since papers mills seldom sell direct to printers and end- users. Distributors often employ design and production consultants who can help printers and their customers choose the right stocks for the job. They may also have customer-service reps to mediate disputes between mills and end-users.

PAPER CHARACTERISTICS (I)

BRIGHTNESS is the measurement of how much white light a paper reflects, expressed as a percentage. No paper reflects 100 percent of the light striking it, but some come close. Premium coated and uncoated white papers and some laser papers are rated as high as 97 percent. Paper for business forms falls somewhere in the 80s–about as low as the lowest rating for any printed product would be. (At the opposite end of the brightness scale are items like brown paper bags, which have a brightness rating of around 20.)Brightness affects readability: too little means low contrast and a dull appearance; too much produces glare and eyestrain. Generally speaking, papers for products like books and technical manuals are less bright than papers for magazines and advertising brochures.OPACITY determines how visible images from the underside of the sheet will be on the side being looked at. A paper should have enough opacity to prevent unwanted images from showing through. Like brightness, opacity is expressed as a percentage, and most printing papers fall within the 80 to 98 percent range (although swatchbooks and price books usually don’t present these ratings–select with care).Mills sometimes add fillers and chemicals to certain papers to increase their opacity. These papers then are marketed as “opaque” grades. Another way to get better opacity is to specify a paper with a higher basis. However, heavier paper costs more to buy and can add to the cost of binding and postage.CALENDERING (note the spelling) is a step in the papermaking process that imparts a smooth surface to the paper. It’s done by running the paper through a stack of calendering rolls–metal cylinders that compress the fibers and reduce the bulk of the paper. “Supercalendering” produces an ultra-smooth, ultra- thin surfaced paper that can be used to print skinny books that have a lot of pages. The trade-offs are loss of opacity and decreased durability.BASIS WEIGHT is the weight in pounds of a ream (500 sheets) in the basic size for that grade. Example: Basis 70 means that a 500-sheet stack of 25×38″ book paper weighs 70 pounds. The basic size is not the same for all grades–each category has a size used to compute its basis weights.The basic size for text, coated, and uncoated papers–in other words, for the papers most widely used in publishing–is 25×38″. Understanding basis weight is important because mills and paper merchants sell paper by the pound, not by the number of sheets or the length of the web.CALIPER is the measurement of a paper’s thickness, expressed as a point size in thousands of an inch. One point equals 1/1000 of an inch. A 7pt. stock is .007″ thick. (A caliper “point” is not the same as a typeface “point,” which is 1/72 of an inch–about 14 times as large.) The smaller the caliper, the more pages per inch (ppi), and vice versa.Caliper is not related to basis weight. Two papers of the same basis weight may be of different thicknesses. That is why we use the term:BULK to refer to a paper’s thickness relative to its basis weight. For example, an uncoated paper might be said to “bulk” higher than coated paper.

PAPER: KINDS, GRADES, BASIC SIZES

Industrywide standard definitions do not exist, but most papers fall into one of five general categories:• BOOK: general-purpose papers for catalogs, magazines, direct mail, and many other kinds of commercial and publication printing.• WRITING: used mainly for stationery.• COVER: thick, heavy stocks for the covers of booklets, manuals, etc.• BRISTOL: thick, stiff papers for business cards, file folders, and other items requiring a durable stock
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• OTHER: papers that do not fit under any of the first four headings, such as onionskin, carbonless duplicating papers, etc.Assigning quality levels to paper is also arbitrary, but the following designations are generally accepted:• The numbers 1 through 5 denote quality grades for coated papers, with #1 being the highest. Coated #1, #2, and #3 papers are free sheets. Coated #4 papers include free sheets and groundwoods. Coated #5 papers are groundwoods. The choice depends on the degree of print quality required. For example, a magazine might use a #2 or #3 sheet for its cover and a #4 or #5 paper for the inside pages.• Other kinds of paper are quality-graded with letters, numbers, and words such as “premium” and “super-premium.” Again, no standard terminology exists.Paper is sold by weight in the “basic size” for its grade. The basic sizes for the four most common grades are:• BOOK: 25″x38″
• WRITING: 17″x22″
• COVER: 20″x26″
• BRISTOL: 22.5″x28.5″

GRAIN DIRECTION

• Paper has “grain” because fibers align themselves in the direction of the wire’s travel through the papermaking machine.

• To test for grain direction, dampen a sheet of paper. It will curl parallel to the grain direction.• A paper is said to be “grain short” when the fibers are parallel to the short dimension (edge) of the sheet; “grain long” when parallel to the long dimension.• Paper always stretches during printing, but it stretches more with the grain than against it. Therefore, printers try to print with the grain parallel to the press cylinders to keep stretch and misregistration to a minimum.• In the bindery, it is better to fold with the grain than against it, since folding against the grain can cause the paper to crack.

THE MAKING OF PAPER

RAW MATERIALS
• Paper is made from fibers of cellulose. The most common source of cellulose is trees, but cellulose from cotton, hemp, and many other materials can be used.• Cellulose from trees contains lignin: “brown stuff” that must be bleached and rinsed out to make printing and writing papers.• Bleaching can leave traces of acid, which is what causes paper to turn yellow and crumble with age. “Acid free” papers contain no acid residue and last much longer.PULPING• Cellulose fibers are separated from wood chips by washing, cooking, and bleaching. The pulp stock (a.k.a. “furnish”) that remains is 99 percent water.”WET END”• In the papermaking machine, the stock is sprayed onto a long, wide, moving screen called a “wire.” Water drains through the wire, and the pulp fibers begin to bond together in a very thin mat on the top side of the wire.• The fiber mat is then squeezed between felt-covered press rollers to absorb more of the water. At this point the “paper” on top of the wire is still about 60 percent water.”DRY END”• The wet paper is heated and dried by passing through a series of steam-filled metal cylinders. Heating and drying the wet sheet seals the fibers together and turns them into finished paper.”CALENDERING” and COATING• The paper is run through a series of smooth-surfaced, chilled metal cylinders known as the “calender.” The calender presses the drying paper smooth and uniform in thickness.• “Supercalendering” the paper through an additional set of rollers gives more smoothness and adds gloss.• Sometimes the paper is coated with a fine clay (kaolin) to fill in surface irregularities. This makes the paper brighter, more opaque, and easier to print on.